Field of the Invention
The present invention relates to an image compositing apparatus, and more particularly, to an image compositing apparatus that superimposes an overlay image on an area of chromakey color on a base image and outputs as a composite image.
Description of the Background Art
There is known an image compositing technique of such a system (referred to as chromakey overlay system) that an image area of a specific color, that is, chromakey color, is drawn on a base image, and an overlay image is subjected to image processing, such as being partially cut out and scaled up or down in accordance with the size and position of the image area for an overlay image, to thereby overlay the overlay image on the image area with the use of chromakey (for example, Japanese Patent Application Laid-Open No. 05-207368 (1993), pp 3 to 5, FIG. 1).
In this case, a part of the base image is set in a chromakey color for overlay, and an overlay image is displayed for pixels in a portion of chromakey color and the base image is displayed per se for pixels in a portion of a color that does not match the chromakey color.
There is known another image compositing technique in such a system (hardware overlay system) that in a case of displaying a plurality of overlay images on a base image, overlay is performed in a display priority order determined in advance for a portion in which the plurality of overlay images are superimposed on each other (for example, Japanese Patent Application Laid-Open No. 2004-355391, pp 3 to 7, FIG. 1).
As a conventional image compositing apparatus obtained by combining the above-mentioned two techniques, there is an image compositing apparatus that overlays and displays a plurality of images in appropriate sizes at appropriate positions on a base image, where the base image is a PC desktop.
This image compositing apparatus creates a composite overlay image obtained by compositing a plurality of overlay images by a hardware overlay system, and thereafter, in a case of compositing the composite overlay image and a base image, composites those images by a chromakey overlay system.
The chromakey color is selected so as not to match the color of a mouse cursor of a PC, and thus, the mouse cursor does not disappear even if the mouse cursor is superimposed on a composite overlay image.
The portion in which a plurality of overlay images are superimposed on each other is composited by the hardware overlay system, which enables to display the plurality of overlay images superimposed in a desired priority order.
The image compositing apparatus obtained by combining the above-mentioned two techniques uses a chromakey overlay system for compositing an overlay image on a base image. For this reason, in a case where there is no signal of the base image, not only the base image cannot be displayed, but also all overlay images cannot be displayed.
If a base image and all overlay images are not displayed in an image compositing apparatus aimed for providing a user with the base image and overlay images as information, an intended function is lost completely. In this respect, a conventional image compositing apparatus has a significant risk in operation.